Santocure.RTM. TBSI (N-t-butyl-2-benzothiazole sulfenimide) is a good replacement for secondary amine based sulfenamide accelerators which are under close environmental scrutiny due to potential nitrosoamine generation during the processing and curing of rubber. Santocure.RTM. TBSI has a long scorch delay and slow cure rate which mimics the secondary amine based sulfenamide accelerators.
It is known to manufacture Santocure.RTM. TBSI from N-t-butyl-2-benzothiazole sulfenamide (Santocure.RTM. NS) and gaseous hydrogen chloride with heptane used as the solvent as shown by the following reaction: ##STR1##
The prior art process involves filtration of heptane slurry to give a crude product which is fully dried and then reslurried in water at 50.degree. C. and then filtered and dried to give a final product. The heptane is recovered by distillation and the heptane still bottoms are incinerated. Thus, this process involves two filtration and two drying steps and recovery of heptane by distillation. This two step filtration/drying process has heretofore been considered to be the only practical means of transferring the Santocure.RTM. TBSI from the solvent phase to the aqueous phase.
For example, U.S. Pat. No. 5,204,481 provides a typical description of the known process in Examples 1 and 2. The reactor mixture is first subjected to a vacuum filtration to separate mixed reaction solids from heptane, the solids are washed and dried and the dry mixed solids are slurried in water to dissolve the hydrochloride salt. The product is then isolated by a further vacuum filtration, water washing and drying.
The prior art process does produce Santocure.RTM. TBSI in high yields and high assay, but as previously mentioned, it demands two filtration and two drying steps. Overall, the prior art process is complicated and inefficient, thereby creating a long felt but heretofore unfulfilled need for process improvements.